Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true and destructiveHint=false, so safety is covered. The description adds two useful behavioral facts: the auth requirement ("Needs the user's Cotlet API key with access to this app") and the fields present in each returned invoice (period, amount, download link), which matters because there is no output schema.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The phrase "with period, amount and a download link" appears twice in consecutive sentences, which is redundant. The description is short overall but not front-loaded with anything the title doesn't already carry.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description usefully enumerates the returned fields (period, amount, download link) and states the auth prerequisite and year default. For a simple one-parameter list tool this is close to complete; only usage-vs-alternatives guidance is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

There is a single parameter with 100% schema description coverage, and the schema already documents the year and its default. The description's "The default is the current year" only echoes the schema, so baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ("Lists the invoices Civitatis issues to you") and clarifies these are commission invoices, which helps distinguish them from the sibling civitatis_list_payments. The first sentence largely restates the title, so it adds scope clarification but no sibling routing beyond the commission-invoice qualifier.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description gives no when-to-use or when-not-to-use guidance and does not point to any alternative tool. It notes the default year and the API-key prerequisite, but these are prerequisites/defaults rather than usage context.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.